1. Field of the Invention
This invention relates generally to a tubular prosthesis and is directed more particularly to a vascular prosthesis adapted to be compliance matched to a vessel or artery in which the prosthesis is implanted.
2. Description of the Prior Art
The development of small vessel prostheses for vascular surgery is known in the art. However, while conventional DACRON.RTM. prostheses maintain long-term patency in large calibers, they are not usable in small sizes. The term DACRON.RTM. is a Trademark for a polyester fiber made from polyethylene terephthalate. Moreover, alternative prostheses, such as those manufactured from various types of bioprosthetic as well expanded TEFLON (ePTFE) synthetic prostheses, which are now available for the reconstruction of smaller and more peripheral arteries such as the coronary and tibial vessels are also inadequate.
Bypasses to the popliteal and infrapopliteal vessels using bioprosthetic umbilical vein prostheses, for example, are complicated by decreased patency and deterioration of the biologic prostheses after three to five years. Similarly, while ePTFE prosthesis initially seemed quite promising experimentally when compared to conventional prostheses, its long term patency in small caliber grafts also has not been acceptable.
In addition, it has long been postulated that the response at the anastomoses of a synthetic prosthesis which has not been perfectly matched to the natural tissue of the host is an important factor in the poor performance of available small vessel prostheses. A vascular prosthesis which is designed to correspond to the exact dimensions and elasticity of the host is thought to lessen the potential for intimal hyperplasia at the anastomoses, an almost universal finding with conventional synthetic vascular prostheses. Intimal hyperplasia is especially compromising to the function of a small caliber prosthesis, since it narrows the already limited available lumen and more significantly alters flow patterns compared to a large caliber vessel.
Both DACRON and ePTFE prostheses have little radial compliance. It would seem reasonable to assume that the pulse pressure in the arterial circulation, which produces distension of the biologic vessels on each heartbeat, creates a boundary condition at the artery/prosthesis junction leading to relative motion between them and stress concentration. That is, the arterial tissue normally distends on each beat, but at the anastomotic site, it is constrained by the rigid prosthesis which does not correspond to the host. This chronic irritation and stress at the anastomoses may result in endothelial injury, smooth muscle cell proliferation, and intimal thickening.
While localized trauma to the host tissue is potentially involved in the development of fibrous intimal hyperplasis, it also has been shown recently that mismatch of the prosthesis with the host results in significantly different flow patterns at the anastomoses even in the absence of localized narrowing of the vessel. These flow disturbances may therefore similarly provide a mechanism responsible for the problems observed at the anastomoses with conventional small vessel prostheses. A further finding has shown that implanted compliant grafts have tended to significantly lose their compliance in vivo during healing.
Therefore, is is desirable for a small caliber prosthesis to retain its compliance properties following healing of the perigraft tissues. The prosthesis must retain its compliance properties in order to minimize its potential to produce intimal hyperplasia or elicit excessive pseudoneointima derived from blood, represented hereinafter by the acronym, PNI, deposition secondary to disturbances of flow patterns at the anastomoses. It was further postulated that to achieve a prosthesis which remains stable with its host, it is important to control healing around the prosthesis so that the prosthesis' compliance properties will remain in a physiologic range.
In one embodiment of the present invention, the exterior textured surface provides for tissue attachment to the implant surface and a diminished foreign body response at the the tissue interface.
There are conventional DACRON prostheses which are textured on both their exterior and interior surfaces, but they do not have radial compliance. DACRON prostheses with an external velour surface were actually tried many years ago, but the function of the external velour was simply to promote more vigorous perigraft tissue in growth through the prosthesis wall to better anchor the PNI.
Replamineform process prostheses are perhaps the most similar textured surface prosthesis to the prosthesis of the present invention, though the prosthesis wall of those prostheses is porous. Made using calcite sea urchin spines as a form for molding a porous elastomeric tube, replamineform prostheses have both porosity and remain stable with their host. Those prostheses are certainly not readily manufacturable, however, nor is their stability with the host easily controlled. Because the wall is uniformly porous, stability with the host can be varied feasibly only over a limited range, and do not remain so when implanted.
Additionally, U.S. Pat. No. 4,731,073 discloses a prosthesis which is constructed from various zones of both solid and porous generally polyether-polyurethane materials. However, the artificial arterial vessel prepared according to the process disclosed in the U.S. Patent is surely larger than that of the conventional small vessel prosthesis. Furthermore, the U.S. Patent discloses the use of a single solid zone only when it is enclosed by non-interfacing porous zones. The compilation of zones disclosed in the U.S. Patent necessarily restricts the potential diameter size of an artificial prostheses, which in turn restricts the degree by which the prosthesis can be matched with its host. Additionally, the interface surfaces are not specifically designed to perform as blood and tissue interfacing surfaces, as in the present invention.
It is therefore an object of the present invention to provide a vascular prosthesis which is readily manufacturable to any length and compliance desired.
It is another object of the present invention to provide a vascular prosthesis which is manufactured from a material which remains stable in vivo.
It is yet another object of the present invention to provide a vascular prosthesis which can be compliance matched to the host vessel.
It is yet another object of the present invention to provide a vascular prosthesis which is designed to retain its compliance following healing of the perigraft tissues.
It is a further object of the present invention to provide a vascular prosthesis with excellent suture retention.
It is still a further object of the present invention to provide a vascular prosthesis available for small vessel prostheses.
It is still a further object of the present invention to provide a vascular prosthesis which will remain uniformly compliant subsequent to healing.